Drakensberg alti-montane grasslands and woodlands
Location and general description
Within this range, the Alti-Montane Grassland and Woodland ecoregion spans the steep and treeless alpine slopes, distinguished from the adjacent montane community by elevations over 2,500 meters, with the highest peaks ranging up to 3480 metres (m). The watershed of the basalt peaks divide water flowing west towards the Atlantic Ocean, or east, down near-vertical slopes into the Indian Ocean. The Drakensberg Range is the source of both the Tugela and Orange Rivers. The Tugela plunges 2000 m over the edge of the Mont-aux-Source Plateau as Tugela Falls. The Orange River is southern Africa’s longest river, originating on the Lesotho Highlands and meandering west forming a natural border between Namibia and South Africa, eventually flowing into the Atlantic Ocean.
Drakensberg basalts, formed at the end of the Triassic, have shallow acidic lithosols and dominate the region’s geology. The basalt forms plateaus and steep slopes with terraces that provide a foundation for treeless alpine vegetation consisting mostly of tussock grasses, creeping or mat-forming plants, and ericoid dwarf shrubs. Rocky mountaintops and precipitous drops, with a few small plateaus, create a variety of habitats with many different plant communities. The Drakensberg forms the southernmost extent of the Afromontane Regional Center of Endemism.
Precipitation averages about 1000 millimetres annually, and temperatures vary from –8° to 32°C, averaging 13°C. Even on hot and sunny days, nighttime temperatures can fall below 0°C. The low temperatures and winter snowfall partially negate the effects of the relatively high rainfall and results in a more arid vegetation cover than may be expected. The temperature extremes combine with fire and strongly influence the extent of the tree/grassland ecotone, but allow for the persistence of Karoid botanical elements.
At lower altitudes, some of the vegetation resembles fynbos, where grass elements are dominated by Bromus speciosus, Festuca costata, Pentaschistis tysonii and Themeda triandra. In the ericaceaous and Afroalpine belts are species of Agrostis, Deschampsia, Festuca, Koeleria, Pentaschistis, and Poa. On the pleateau, dominant and diagnostic grass species include Merxmuellera disticha, M. drakensbergensis, Festuca caprina, Eragrostis caesia, Poa binata, and Pentaschistis galpinii. Non-grassy forbs include Carex clavata, Scirps falsus, Helichrysum flanaganii, H. trilineatum, H. witbergense, and Erica frigida.
The montane habitats of Africa are principally scattered along a 5000 kilometre long mountain chain running from the Ethiopian Plateau in the north to the coastal areas of South Africa. To the west are isolated mountain areas in Angola and Cameroon. While some of these montane habitats are within visual distance of each other, others are separated by hundreds of kilometers. Yet, in nearly all cases, the intervening vegetation appears to form an effective barrier to dispersal for species confined to these high altitude environments. The montane habitats of Africa can thus be considered as ecological islands. The Drakensberg forms the southernmost extent of this mountainous chain and while not as high in elevation as some of the mountains at the equator, the higher latitude compensates for the lower elevation.
Some of Africa’s oldest centres of plant endemism are associated with the Drakensberg Mountains. While the number of plant species solely restricted to the high Drakensberg is unknown, within the KwaZulu-Natal region of the Drakensberg, 1750 vascular plant species have been recorded. Of these, 394 species are endemic to the southern Drakensberg (22.5 percent Hillard and Burt 1987). The highest levels of endemism occur on the highest peaks. For example, Helichrysum palustre has been recorded only from the summit plateau of the Drakensberg and the high mountains in Lesotho between 2300 and 3400 m. The spiral aloe (Aloe polyphylia), a spectacular endemic plant of Lesotho, is found only above 2000 m.
The alti-montane habitats of the Drakensberg have only about 20 vascular plant species in common with the Afroalpine flora of east and northeast Africa. The region lacks the conspicuous alpine giant lobelias (Lobelia spp.) and giant senecios (Dendrosenecio spp.) of the high mountains of central and eastern Africa. It is likely that the seasonal climate and unique ecological conditions in the Drakensberg explains the lack of these characteristic East and Central African Afroalpine floral elements. Moreover, the giant lobelias and giant senecios have evolved and radiated relatively recently from an East African ancestor, making their presence in the Drakensberg unlikely.
Three river frogs: Sani Pass Frog (Amietia dracomontana), Large-mouthed Frog (Amietia vertebralis), and Cape River Frog (Amietia fuscigula) are endemic to rapidly-flowing streams of the alti-montane grassland. Other anurans found in the ecoregion are the Dwarf African Toad (Poyntonophrynus vertebralis), a toad found only in this ecoregion and the Highveld grasslands.
Grass banks next to alti-montane rivers are also home to the recently described Cream-spotted Mountain Snake (Montaspis gilvomaculata), the only member of its genus. The high alpine moors are home to three endemic lizard species, including one listed in the South African Red Data Book, Lang's Girdled Lizard (Pseudocordylus langi), as well as Cottrell's Mountain Lizard (Tropidosaura cottrelli) and Essex's Mountain Lizard (T. essexi). The ecoregion also supports important populations of another endangered species of lizard, Breyer’s Long-tailed Lizard (Tetradactylus breyeri), the main populations of two restricted-range lizards: the Five-toed Whip Lizard (Tetradactylus seps) and the Drakensberg Crag Lizard (Pseudocordylus melanotus), as well as two near-endemic geckos (Afroedura karroica halli) and the Drakensberg Rock Gecko (A. nivaria).
In the Drakensberg, about 250 species of birds have been recorded. The mountain pipit (Anthus hoeschi) is endemic to this ecoregion. Another six species are near-endemic, including bush blackcap (Lioptilus nigricapillus), buff-streaked chat (Saxicola bifasciata), Rudd’s lark (Heteromirafra ruddi, CR), orange-breasted rockjumper (Chaetops aurantius), yellow-breasted pipit (Anthus chloris, VU), and Drakensberg siskin (Serinus symonsi). The southern bald ibis (Geronticus calvus VU), Cape vulture (Gyps coprotheres VU) and wintering lesser kestrel (Falco naumanni VU) are other globally threatened bird species that occur in the ecoregion.
The area is home to a variety of ungulates, including the Klipspringer (Oreotragus oreotragus), Mountain Reedbuck (Redunca fulvorufula), and Eland (Taurotragus oryx). The Tsoelikana River harbors the Endangered Drakensberg Minnow (Pseudobarbus quathlambae), which was until recently thought to be extinct.
Along with spectacular flora and fauna, the Drakensberg region is especially rich in cultural heritage. Thousands of Bushman painting sites from the primitive San people dating as far back as 800 years ago are scattered through the mountains.
The high altitude streams, oxbow lakes, wetlands, and high annual rainfall of the ecoregion have been recognized as being very important for providing water for the urban and industrial complexes in the South African provinces of Mpumalanga and Gauteng, which contains Johannesburg.
At the highest elevations in rocky areas, habitats are relatively intact. However, at lower elevations, areas not designated as protected are severely threatened. Heavy grazing pressure by domestic species alters the ecosystem and makes the existing habitats vulnerable to encroachment by vegetation found in Karoo. It has been estimated that by 1986, more than 37 percent of the original extent of the Afromontane vegetation had been transformed, mostly from the clearing of forest on lower slopes for agriculture and timber production. The stocking rates of grazing animals in Lesotho are currently estimated to exceed carrying capacity by 300 percent.
In the Drakensberg alpine region 193.6 km2 (3 percent in Lesotho and 97 percent in the Natal Drakensberg) are protected as nature reserves, national parks and wilderness areas. Since 1985, negotiations have aimed at the establishment of the Maloti/Drakenserg Trans-Frontier Conservation Area. This would include the existing Maloti/Drakenserg Peace Park that spans some 8,100 km2 of mountains, amounting to the most important high-elevation protected area on the subcontinent. On the South African side of the border between Royal Natal National Park and Cathedral Peak, the continuity of the protected area is fragmented by the amaNgwayne Tribal area. However, local community members have shown interest in incorporating a variety of ecotourism programs that would be compatible with the park. On the Lesotho side, IUCN ranks the Sehlabathebe National Park as a schedule IV protected area. Currently a Lesotho Highlands Water Project is under construction. Expected key outputs include comprehensive strategies for livestock husbandry, natural resource conservation, ecotourism, environmental education and extension, and sustainable land use. However, these developments will have to be evaluated in context with the altered flow regimes of the Orange River and associated watershed basins, along with the potential perils of the introduction of exotic species via inter-basin water transfer schemes.
Types and Severity of Threats
The greatest threats posed to high altitude vegetation are from the impacts associated with mountain climbers and walkers treading on the vulnerable and rare plant species, which live in inhospitable climatic and topographic circumstances. Well-maintained trails that keep people out of fragile areas in addition to designated campsites may help to reduce impact. However, at lower elevations, heavy grazing pressure by domestic species and the clearing of forest for agriculture and timber production are serious threats. Other concerns include invasive exotic plants like the unpalatable shrubs Chrysocoma ciliata and Helichrysum trilineatum, severe soil erosion, and clearance for crops on agriculturally poor land.
Justification of Ecoregion Delineation
The boundaries of this ecoregion follow the altimontane vegetation in southern Africa, mapped by White, and the ‘alti mountain grassland’ unit and Low and Rebelo, following the 2500 m elevation contour. Although it lacks the giant Lobelia and Dendrosenecio species of the altimontane areas in eastern Africa, it supports a number of endemic plants in the highest elevations.
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